But the game estabishes a limit to the distance that a character moves per turn yet violates that when moving captives. That is why I go Huh at this. Is it a game buster, no. But it does seem to be a contradiction within the game.
It is a contradiction with a clear reason for it:
If you were to take 6 days moving to prison, it would be boring and not fun, and add nothing meaningful to the game.
Think about it. 6 days on the way there, 7 days sitting in prison, and then another 6 days back to the capital—or instantly transported to prison, 7 days sitting there, and then 1 turn back to your capital.
Which would you really prefer? Particularly since your actual prison options wouldn't be available until you
got to prison.